The optic nerve - Disorders of cranial nerves

The optic nerve

Anatomy

The optic nerve carries information from the retina via the optic chiasm, the lateral geniculate bodies and optic radiation to the occipital lobe where the visual cortex is situated.

Function

Vision

Clinical features

These depend on the location of the lesion (see Fig. 7.4).

Field loss:

·        Eye lesions include diabetic retinal vascular disease, glaucoma, retinitis pigmentosa.

·        Optic nerve lesions include multiple sclerosis, compression, syphilis, ischaemia, B12 deficiency.

·        Optic chiasm lesions commonly caused by pituitary neoplasm, rarely secondary neoplasm.

·        Optic tract lesions alone are rare but commonly occur as part of a middle cerebral artery stroke.

·        Optic cortex lesions (macula spared) caused by posterior cerebral artery infarction. Widespread bilateral occipital damage, e.g. posterior circulation infarction causes cortical blindness (Anton’s Syndrome) in which the patient lacks insight and denies blindness.

·        Tunnel vision occurs in other conditions, e.g. in glaucoma or late retinitis pigmentosa.

Diseases affecting the optic nerve and the rest of the optic pathways may also affect visual acuity.